1. Field of the Invention
The present invention relates to a command input control system, and to a method for controlling input of commands to a multimedia communication terminal device of a type used for reproducing entertainment or educational software which has been transmitted through a communication line. More specifically, the invention relates to a command input control system and control method for use where a plurality of commands, for example, for initiating respective reproduction modes, potentially may be sequentially input within a short period by the user.
2. Description of the Related Art
Currently, development of a television service known as VOD (Video On Demand) using a communication line, such as a cable television (CATV) system, is in progress. In such a service, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. Heisei 4-324784, one end of a transmission line is connected to a recording medium or a recording apparatus which supplies and controls the supply of multi-media data, known as a head end apparatus. The other end of the transmission line is connected to one or more multi-media communication terminal devices, such as a set top box (STB) installed for each subscriber. The STB is connected to a television set or television receiver having a display and an interface to receive the VOD service. Currently, development of such systems by developers is ongoing.
In such a multi-media communication system employing a communication network, when a command is input in the form of an interrupt signal to the multi-media communication terminal device from a superior system, such as the head end apparatus mentioned above, it is possible for the interrupt signal to cause dropping out and disturbance of the video data and sound data which are being reproduced currently. Therefore, in order to avoid this problem, Japanese Unexamined Patent Publication No. Showa 63-209243 discloses a technology for pausing the multi-media data which is being reproduced currently from the superior system, then subsequently releasing the pause mode upon termination of the interrupt process, and then again initiating transmission of the multi-media data.
On the other hand, when a command for changing to a new reproduction mode, for example, is input by the subscriber, to the multi-media communication terminal device, it becomes necessary to avoid a disturbance of the video image which is associated with switching into the new reproduction mode. Particularly when switching to a reproduction speed which is lower than a normal reproduction speed, such as slow motion reproduction, or field search (field-by-field reproduction), the possibility of causing such disturbance becomes high. As a solution for this, it may be possible to control the amount of multi-media data transmitted from the superior device and to transmit only a predetermined amount of data at every occurrence of a demand for data transmission from the multi-media communication terminal device.
In the conventional multi-media communication service using the communication line as described above, if the commands relating to the reproduction mode of the multi-media data are sequentially input by the user within a short period of time, it becomes possible to cause a disturbance in the reproduced video image or audio sound or to output an unintended image or sound. Also, when synchronization of the video image and the audio sound is included in the reproduction mode requested by the user, an error in synchronization of the video image and the audio sound is likely to occur.
Therefore, it becomes necessary to exercise control over input commands so as not to cause disturbance in the video image even when the commands are sequentially input within a short period.